Effects of nitroglycerin on left ventricular volumes and wall tension in patients with ischaemic heart disease

Since the dimensions of the ventricles are related to both myocardial tension and myocardial oxygen consumption (MVO2), the effects of nitroglycerin on the left ventricular volumes and left ventricular haemodynamics were studied in patients with ischaemic heart disease. The ventricular volumes were estimated using the constant infusion technique (indocyanine green) of Shaffer (1964). Sublingual administration of nitroglycerin (0.6 mg.) resulted in a significant reduction in cardiac output (27%), mean systolic pressure (21%), left ventricular end-diastolic pressure (63%), stroke volume (27%), left ventricular end-diastolic volume (26%), and left ventricular work (41%). Both calculated circumferential myocardial force (40%) and the myocardial tension (33%) decreased during systole, while the pressure-time index decreased by 27%. A similar decrease was also found in the contractile element work (42%), and mean circumferential fibre shortening rate (22%). Thus, this study has shown that the major determinants of MVO2, i.e. myocardial wall tension, the velocity of contraction, and contractile element work, decrease significantly after administration of nitroglycerin.

Hemodynamic changes following correction of severe aortic stenosis using the Cutter-Smeloff prosthesis

Twelve patients with pure or dominant stenosis were studied before and after aortic valve replacement (Cutter-Smeloff). The changes in cardiac output and A-V O2 difference were small and insignificant, but exercise stroke volume increased from 72 to 96 ml after the surgery. The aortic peak systolic gradient was 92 +/- 29 mm Hg before and 4 +/- 9.8 mm Hg after surgery. The PA wedge pressure, taken as a measure of the LV diastolic pressure, decreased from 18 mm Hg to 12 mm Hg at rest and 30 mm Hg to 16 mm Hg on exercise. The PA pressures also decreased from 37/18 (mean, 26) to 28/11 (17) mm Hg at rest, and 61/31 (43) to 41/17 (27) mm Hg on exercise, but the PA and PA wedge pressures maintained their tendency to increase in a linear manner with oxygen consumption (Vo2) on exercise after surgery. As a result of decreased wedge pressure, the pulmonary vascular resistance also decreased significantly afterward. The adequacy of cardiac output at rest and on exercise expressed by cardiac output as the linear function of Vo2 improved toward the normal (values before operation, CO = 2.78 + 0.0069 Vo2, r = 0.84; after operation, CO = 3.80 + 0.0062 Vo2, r = 0.91). The exercise factor (delta CO/delta Vo2) or the regression coefficient, however, was similar before and after surgery. The hemodynamic result was satisfactory although some abnormalities of the left ventricular function persisted after operation.

Malfunction of the mitral valve prosthesis (Cutter-Smeloff). Clinical and hemodynamic observations in three cases

Three cases of intermittent obstruction of the mitral prosthesis (Cutter-Smeloff) due to ball variance have been reported. The typical findings were marked variation in the arterial pulse and the intensity of the mitral closing sound and intermittent absence of the opening click. The phonocardiography revealed varying intervals from aortic closing sound to the opening click (A 2 - OC interval). Hemodynamic studies revealed fluctuating aortic and pulmonary artery wedge pressures in spite of normal sinus rhythm, due to impaction of the ball into the prosthetic ring, opening only with severe elevation of the left atrial pressure. At operation, the balls showed yellowish discoloration, but no disruption of sutures nor thrombosis of the prosthesis was found. The incidence of this phenomenon was 9% with the Cutter-Smeloff mitral prosthesis, but no such case was seen among patients with the Starr-Edwards mitral prosthesis.